Currently, there are two synthesis examples of cycloparaphenylenes. One is Bertozzi (USA, UC Berkeley) et al., who first succeeded in synthesizing cycloparaphenylenes (n=5, 8, 14) containing 9, 12, or 18 phenylenes in the following manner (NPL 1).

The feature of this method is to use sp3 carbons of cis-substituted cyclohexadiene-1,4-diol (compound 4) to form curves required for cycloparaphenylene, followed by conversion to sp2 carbons in the last step. This method has drawbacks in regard to low yield and low selectivity, including the time of producing ring products.
Itami (Nagoya University) et al. has reported the following method for selectively synthesizing cycloparaphenylene consisting of 12 benzene rings (NPL 2).

In this method, cis-cyclohexane-1,4-diol was used to form curves, and the compound was converted to sp2 carbon in the last step. Only cycloparaphenylene having 12 phenylenes can be selectively obtained; however, it is unclear whether compounds having other numbers of rings can be synthesized.
In both synthesis examples, the reaction conditions of the aromatization reaction in the last step are severe. More specifically, Bertozzi et al. used lithium naphthalenide (strongly basic), while Itami et al. added para-toluenesulfonic acid (highly acidic), followed by heating at 150° C.; accordingly, these methods are not suitable for the synthesis of cycloparaphenylene derivatives having various functional groups.